A methanol plant requires large quantities of natural gas feed from a high pressure transmission network. A portion of this natural gas feed is reduced in pressure through a control valve to low pressure and burned as fuel in the Steam Methane Reformer (SMR), and/or fired heater, and/or gas turbine, auxiliary boiler, steam boiler, and auxiliary burners.
The remaining portion (and majority) of the natural gas feed is processed in desulfurization unit, and reacted in SMR and/or ATR (Autothermal Reformer) to produce a syngas. In a methanol plant the syngas is further compressed to approximately 50-150 bara and reacted to produce methanol and a pressurized byproduct stream that is hydrogen rich. This byproduct stream can be split into two fractions, with the first fraction going to a Pressure Swing Adsorber (PSA) to produce a purified hydrogen product, and the remaining second fraction, also referred to as a purge gas, is reduced in pressure with a control valve to approximately 0.3-7 bara and used as fuel within the methanol plant.
With respect to air separation units (ASU), oxygen and nitrogen are separated from atmospheric air by cryogenic distillation. The required separation energy is provided by a main air compressor (MAC). The oxygen (and possibly nitrogen) product compression is provided by pumping the cryogenic liquid and vaporizing at the required product pressure in the main ASU heat exchanger. The energy required for this product vaporization, as well as energy required for liquefied products, is provided by a booster air compressor (BAC).